Definition

BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down.

A test can be done to measure the amount of urea nitrogen in the blood.

Alternative Names

Blood urea nitrogen

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood.

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants and young children, the area is cleaned with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test

Some drugs affect BUN levels. Before having this test, make sure the health care provider knows which medications you are taking.

Drugs that can increase BUN measurements include:

• Allopurinol
• Aminoglycosides
• Amphotericin B
• Bacitracin
• Carbamazepine
• Cephalosporins
• Chloral hydrate
• Cisplatin
• Colistin
• Furosemide
• Gentamicin
• Guanethidine
• High-dose aspirin
• Indomethacin
• Methicillin
• Methotrexate
• Methyldopa
• Neomycin
• Penicillamine
• Polymyxin B
• Probenecid
• Propranolol
• Rifampin
• Spironolactone
• Tetracyclines
• Thiazide diuretics
• Triamterene
• Vancomycin

Drugs that can decrease BUN measurements include:

• Chloramphenicol
• Streptomycin

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

The BUN test is often done to check kidney function.

Normal Values

7 - 20 mg/dl. Note that normal values may vary among different laboratories.

Reviewer Info: Robert Mushnick, M.D., Clinical Assistant Professor, Department of Nephrology, SUNY Downstate Health Center, Brooklyn, NY. Review provided by VeriMed Healthcare Network., 05/15/2007